Method for making multi-layer preform used for plastic blow molding

ABSTRACT

A multi-layer preform (26a,26b,26c) used for plastic blow molding and a method for making the preform provides an inner layer (28) of polyethylene naphthalate and an injection molded outer layer (30) of polyethylene terephthalate which has reduced transmission of gas upon blow molding as a container due to the gas barrier provided by the inner layer of polyethylene naphthalate. The inner layer (28) of polyethylene naphthalate by itself or along with a further inner layer (32) of virgin polyethylene terephthalate is thermoformed prior to the injection molding of the outer layer (30) of polyethylene terephthalate. A minimal amount of the polyethylene naphthalate which is relatively expensive can be utilized due to the thermoforming and injection molding as disclosed.

This is a continuation of application Ser. No. 08/120,038 filed on Sep.10, 1993 and issued on Aug. 22, 1995 as U.S. Pat. No. 5,443,766.

TECHNICAL FIELD

This invention relates to a multi-layer preform used for plastic blowmolding and to a method for making the preform.

BACKGROUND ART

Plastic blow molding is conventionally performed by providing a hotplastic parison either from extruded plastic or as a preform which isusually injection molded from plastic. Usually, such preforms arecomposed of a single type of plastic that is injected into a moldthrough a single port. However, there have also been attempts to providecoinjection of more than one plastic into a mold so as to providedifferent layers of plastic.

U.S. Pat. No. 3,878,282 to Bonis et al. discloses a process for moldingmulti-layer articles that are specifically disposed as a preform-typeparison with different layers. The process involved is performed byinjection molding the different layers within different molds whilemounted on the same inner mandrel during the injection of each layer.

U.S. Pat. No. 4,307,137 to Ota et al. discloses a method for forming anoptical design pattern in polyethylene terephthalate articles which arespecifically disclosed as a blow molding preform having inner and outermembers with the inner member having an open end defining a threadclosure and with the outer member having a junction with the innermember toward a closed end of the preform from the thread closure.

U.S. Pat. No. 4,391,861 to Nilsson discloses a preform of athermoplastic and has a two-part interfitted construction and at leastone intermediate layer that functions as a gas barrier, and alsodiscloses that the outer part may be previously used and reprocessedmaterial.

U.S. Pat. No. 4,646,925 to Nohara discloses a multi-layer preform fordraw-blow forming a bottle which has inner and outer layers with ajunction that is located toward a closed end of the preform from aclosure thread at an open end of the preform. The preform also includesa gas barrier intermediate the inner and outer layers.

U.S. Pat. No. 5,102,705 discloses a bottle made of polyethylenenaphthalate resin produced by highly stretching a preform in a mannerthat is disclosed as limiting gas permeability and x-ray transmission.

There have been attempts in the past, such as disclosed by theaforementioned Nilsson patent, to utilize post consumer recycled plasticfor plastic blow molding since such reuse reduces the need foradditional land fills as well as conserving on natural resources in themanufacturing of new articles. Such prior attempts have utilizedinjection molding or extrusion which necessarily limits the amount ofpost consumer recycled plastic which can be utilized since it isdifficult to injection mold or extrude relatively thin wall preformsused for plastic blow molding. The maximum amount of post consumerrecycled plastic which has been used to date is about 50% by weight ofthe total weight of the preform.

Blow molding has also previously been performed utilizing a preform thatis initially thermoformed from film, i.e. sheet plastic, that provides amoisture and/or oxygen barrier prior to injection molding of an outerprotective layer. After the thermoforming, the formed film is trimmedand the outer layer is then injection molded around the thermoformedplastic prior to the finished preform being blow molded to provide theresultant container.

The dominant gas barrier commercially utilized at the present time toprevent gas transmission through blow molded containers is ethyl vinylalcohol which may be dipped, sprayed or brushed as well as coinjectedwith plastic resin. One disadvantage of ethyl vinyl alcohol is that itmust be fully enveloped by the plastic of the preform or it will tend todraw moisture from the atmosphere and thereby loses its ability tofunction in preventing gas transmission through the container.

DISCLOSURE OF INVENTION

One object of the present invention is to provide an improvedmulti-layer preform used for plastic blow molding.

In carrying out the above object, the multi-layer preform used forplastic blow molding has an inner layer of polyethylene naphthalate forproviding a gas barrier. The preform also has an injection molded outerlayer of polyethylene terephthalate which, upon blowing of the preforminto a container, has reduced transmission of gas due to the gas barrierprovided by the inner layer of polyethylene naphthalate.

It is possible for the multi-layer preform used for plastic blow moldingto be constructed with the inner layer consisting essentially only ofthe polyethylene naphthalate or as a mixture of the polyethylenenaphthalate and a further resin. The further resins which may beutilized can be polyolefins, polyamides, polycarbonates,polyesteramides, polyesters and combinations of these resins. Morespecifically, the further resin may be polyethylene terephthalate fromwhich the outer layer is also injection molded. Use of such furtherresins while somewhat decreasing the gas barrier properties of the innerlayer reduces the amount of polyethylene naphthalate utilized which issubstantially more expensive than the polyethylene terephthalate andother resins.

In one embodiment, the preform is constructed with the outer layer ofpolyethylene terephthalate injection molded from virgin polyethyleneterephthalate. In this embodiment, the inner layer of polyethylenenaphthalate and the outer layer of virgin polyethylene terephthalatehave a direct interface with each other.

In other embodiments of the preform, the outer layer is injection moldedfrom post consumer recycled polyethylene terephthalate. Such furtherembodiments are also disclosed as having a further inner layer of virginpolyethylene terephthalate that cooperates with the inner layer ofpolyethylene naphthalate in separating the outer layer of post consumerrecycled polyethylene terephthalate from the contents of the containerthat is blow molded from the preform. In one such embodiment, thefurther inner layer of virgin polyethylene terephthalate is locatedbetween the inner layer of polyethylene naphthalate and the outer layerof post consumer recycled polyethylene terephthalate. In another suchembodiment, the inner layer of polyethylene naphthalate is locatedbetween the inner layer of virgin polyethylene terephthalate and theouter layer of post consumer polyethylene terephthalate.

Another object of the invention is to provide an improved method formaking a multi-layer preform used for plastic blow molding.

In carrying out the immediately preceding above object, the improvedmethod for making a multi-layer preform used for plastic blow molding isperformed by thermoforming a sheet of polyethylene naphthalate toprovide an inner layer that functions as a gas barrier. Injectionmolding of an outer layer of polyethylene terephthalate is performedaround the inner layer of polyethylene naphthalate which limits thetransmission of gas through the outer layer of polyethyleneterephthalate upon blow molding of the preform into a container.

In one practice of the method, the injection molding of the outer layeris performed with virgin polyethylene terephthalate that has a directinterface with the inner layer of polyethylene naphthalate.

Further practices of the method are performed utilizing a sheet ofvirgin polyethylene terephthalate that is thermoformed to provide afurther inner layer that has a direct interface with the inner layer ofpolyethylene naphthalate, and the injection molding is subsequentlyperformed about the inner layers utilizing post consumer recycledpolyethylene terephthalate. The sheets of polyethylene naphthalate andvirgin polyethylene terephthalate are preferably thermoformedsimultaneously with each other. The thermoformed sheets of polyethylenenaphthalate and virgin polyethylene terephthalate are most preferablytransferred together with each other to the injection mold for theinjection molding of the post consumer recycled polyethyleneterephthalate. In one practice, the thermoforming is performed toprovide the inner layer of virgin polyethylene terephthalate between theinner layer of polyethylene naphthalate and the outer layer of postconsumer recycled polyethylene terephthalate. In another practice, thethermoforming is performed to provide the inner layer of polyethylenenaphthalate between the inner layer of virgin polyethylene terephthalateand the outer layer of post consumer recycled polyethyleneterephthalate.

The objects, features and advantages of the present invention arereadily apparent from the following detailed description of the bestmodes for carrying out the invention when taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a partially broken away side elevational view of a plasticblow molded container formed from a preform according to the presentinvention;

FIG. 2 is an elevational sectional view of one embodiment of a preformthat is constructed in accordance with the present invention to includean inner layer of polyethylene naphthalate and an outer layer of virginpolyethylene terephthalate;

FIG. 2a is a partial sectional view of the preform shown in FIG. 2 butat an enlarged scale;

FIG. 3 is an elevational view taken in section of another embodiment ofthe preform which includes an inner layer of polyethylene naphthalate, afurther inner layer of virgin polyethylene terephthalate and aninjection molded outer layer of post consumer recycled polyethyleneterephthalate with the inner layer of virgin polyethylene terephthalatelocated between the inner layer of polyethylene naphthalate and theinjection molded outer layer of post consumer recycled polyethyleneterephthalate;

FIG. 3a is a partial sectional view of the preform shown in FIG. 3 butat an enlarged scale;

FIG. 4 is an elevational sectional view of another embodiment of thepreform which includes an inner layer of polyethylene naphthalate, afurther inner layer of virgin polyethylene terephthalate and aninjection molded outer layer of post consumer recycled polyethyleneterephthalate with the inner layer of polyethylene naphthalate locatedbetween the inner layer of virgin polyethylene terephthalate and theinjection molded outer layer of post consumer recycled polyethyleneterephthalate;

FIG. 4a is a partial sectional view of the preform shown in FIG. 4 butat an enlarged scale; and

FIG. 5 is a view that illustrates the method for making the FIG. 2embodiment of the preform by thermoforming and subsequent injectionmolding;

FIG. 6 is a view that illustrates the method for making the preformembodiments of FIGS. 3 and 4 by thermoforming and subsequent injectionmolding;

FIG. 7 illustrates the manner in which the method is performed in FIG. 6to make the FIG. 3 embodiment of the preform wherein the inner layer ofpolyethylene naphthalate is located inside of the inner layer of virginpolyethylene terephthalate; and

FIG. 8 is a view that illustrates the manner in which the method isperformed in FIG. 6 to make the FIG. 4 embodiment of the preform whereinthe inner layer of virgin polyethylene terephthalate is located insideof the inner layer of polyethylene naphthalate.

BEST MODES FOR CARRYING OUT THE INVENTION

With reference to FIG. 1 of the drawings, a plastic blow moldedcontainer generally indicated by 10 is blow molded from a multi-layerpreform constructed according to the present invention as is hereinaftermore fully described. The plastic blow molded container 10 includes acylindrical body portion 12 that extends vertically. An upper endclosure 14 of the container is unitary with the upper extremity of thecylindrical body portion 12 and includes a dispensing spout which isillustrated as having a thread 16 for securing an unshown cap-typeclosure. The container also includes a freestanding base structure 18unitary with the cylindrical body portion 12 to close its lowerextremity. The freestanding base structure 18 further includes aplurality of downwardly projecting hollow legs 20 (only one shown)spaced circumferentially from each other with respect to the bodyportion. The freestanding base structure 18 also includes a plurality ofcurved ribs 22 (only one shown) spaced circumferentially from each otherbetween the downwardly projecting legs 20. The freestanding basestructure 18 of the container also includes a central hub 24 with thelegs 20 and curved ribs 22 extending radially therefrom in acircumferentially alternating relationship to each other. Of course, itshould be understood that while the container illustrated is of thefreestanding type with legs and curved ribs, other freestandingcontainers without legs and curved ribs as well as containers that havea lower base cup for support can also be blow molded from preformsaccording to the present invention as described below.

With reference to FIGS. 2, 3 and 4, three preferred embodiments of amulti-layer preform 26a, 26b and 26c used for plastic blow molding areeach constructed with a vertically extending tubular shape having alower closed end and has an upper open end from which the container 10shown in FIG. 1 is blow molded. This blow molding is preferablyperformed by stretch blow molding to provide biaxial orientation of thecontainer wall so as to have enhanced strength. While the multi-layerpreforms 26a, 26b and 26c have different constructions as is hereinaftermore fully described, each preform has an inner layer 28 of polyethylenenaphthalate for providing a gas barrier and also has an injection moldedouter layer 30 of polyethylene terephthalate which, upon blowing of thepreform into the container as described above, has reduced transmissionof gas due to the gas barrier provided by the inner layer ofpolyethylene naphthalate. As hereinafter more fully described, the innerlayer 28 of polyethylene naphthalate is thermoformed which permits arelatively thin wall to be provided as compared to injection molding.

Polyethylene naphthalate has a greater ability to prevent gastransmission than does polyethylene terephthalate, especially withcarbon dioxide and oxygen wherein only about 1/8 or so and 1/5 or so,respectively, of the gas will permeate through polyethylene naphthalateas compared to polyethylene terephthalate. It is also possible toprovide stretch blow molding of polyethylene naphthalate so it can bebiaxially oriented with the polyethylene terephthalate in themulti-layer preform constructions disclosed. Furthermore, it should alsobe appreciated that polyethylene naphthalate can be hot filled and thusis useful for food processing or other processing whose contents areheated upon filling.

Each embodiment of the preform 26a, 26b and 26c may have the inner layer28 of polyethylene naphthalate consisting essentially only of thepolyethylene naphthalate or as a mixture of polyethylene naphthalate anda further resin. Possibilities of the further resin utilized arepolyolefins, polyamides, polycarbonates, polyesteramides, polyesters andcombinations of these resins. More specifically, the use of polyethyleneterephthalate which is a polyester while reducing the gas barrierproperties somewhat still allows the polyethylene naphthalate tofunction as a gas barrier while decreasing the extent of thepolyethylene naphthalate required so as to permit recycling of the usedcontainer and limiting the extent of non-polyethylene terephthalate aspart of the container. Such limitation of the non-polyethyleneterephthalate percentage of the container allows it to fall into a moreselect classification as part of the recycling. More specifically, for acertain classification, it is necessary for the non-polyethyleneterephthalate to be less than about 11/2% by weight of the totalcontainer weight.

With specific reference to FIG. 2, the multi-layer preform 26a has theouter layer 30 of polyethylene terephthalate injection molded fromvirgin polyethylene terephthalate. Furthermore, the inner layer 28 ofpolyethylene naphthalate of this embodiment of the preform and the outerlayer 30 of virgin polyethylene terephthalate have a direct interfacewith each other. With this construction, the extent of polyethylenenaphthalate utilized need only be sufficient to provide the required gasbarrier properties for the resultant container. As such, the amount ofpolyethylene naphthalate can be reduced as permitted to meet recyclingclassifications. Furthermore, since the end closure 14 of the resultantcontainer is thicker than the rest of the container and the outer layer30 is virgin polyethylene terephthalate, the inner layer 28 ofpolyethylene naphthalate can terminate below the upper extremity of theouter layer 30 of polyethylene terephthalate without greatly reducingthe gas barrier capability of the container and while still allowing thecontainer to be used for food or beverages.

With reference to FIGS. 3 and 4, each of the embodiments of the preform26b and 26c has the outer layer 30 thereof injection molded from postconsumer recycled polyethylene terephthalate. Each of the embodiments ofthe preform 26b and 26c also includes a further inner layer 32 of virginpolyethylene terephthalate that cooperates With the inner layer 28 ofpolyethylene naphthalate in separating the outer layer 30 of postconsumer recycled polyethylene terephthalate from the contents of thecontainer that is blow molded from the preform. With the FIG. 3embodiment of the preform 26b, the further inner layer 32 of virginpolyethylene terephthalate is located between the inner layer 28 ofpolyethylene naphthalate and the outer layer 30 of post consumerrecycled polyethylene terephthalate. With the FIG. 4 embodiment of thepreform 26c, the inner layer 28 of polyethylene naphthalate is locatedbetween the inner layer 32 of virgin polyethylene terephthalate and theouter layer 30 of post consumer recycled polyethylene terephthalate. Useof the further inner layer 32 of virgin polyethylene terephthalate incooperation with the inner layer 28 of polyethylene naphthalate in boththe FIG. 2 and the FIG. 3 embodiments of the preform allows minimal useof the polyethylene naphthalate to provide the required gas barrierneeded while still providing wall thickness separation from the outerlayer 30 of post consumer recycled polyethylene terephthalate in orderto meet standards set by regulatory agencies in connection withcontainers made from recycled resin.

With reference to FIGS. 5 and 6, apparatus 34a and 34b,c respectivelyoperate to perform the method for making a multi-layer preform used forplastic blow molding as illustrated by the embodiment 26a of FIG. 2 andthe embodiments 26b and 26c of FIGS. 3 and 4. More specifically, each ofthe embodiments of the apparatus 34a and 34b,c includes a thermoformingstation 36 for thermoforming a sheet 38 of polyethylene naphthalate toprovide the inner layer 28 of polyethylene naphthalate with theelongated tubular construction having a closed end and an open end aspreviously described in connection with FIGS. 2-4. Suitable heaters 40heat the sheet 28 of polyethylene naphthalate which is essentially afilm of the required thickness prior to the thermoforming at thethermoforming station 36. Rolls 42 move the sheet 38 of polyethylenenaphthalate along the apparatus from the left toward the right asillustrated. After the thermoforming as is hereinafter more fullydescribed, the sheet 38 of polyethylene naphthalate is moved to atrimming station 44 where the upper open end of the inner layer 28 ofpolyethylene naphthalate is cut from the rest of the sheet forsubsequent transfer as is hereinafter more fully described to aninjection molding machine 46. Thereafter, the injection molding of theouter layer of polyethylene terephthalate is performed around the innerlayer of polyethylene naphthalate which, as previously described, limitsthe transmission of gas through the outer layer of polyethyleneterephthalate upon blowing of the resultant preform into a container.

Use of the apparatus 34a as illustrated in FIG. 5 is performed with thesheet 38 of the polyethylene naphthalate thermoformed by itself at thethermoforming station 36 prior to being trimmed at the trimming station44 and transferred to the injection molding machine 46 where the outerlayer 30 of polyethylene terephthalate is injection molded. Morespecifically, in order to maintain as little polyethylene naphthalate aspossible as part of the preform, it is preferable for the apparatus 34ato perform the method by injection molding the outer layer 30 fromvirgin polyethylene terephthalate.

Apparatus 34b,c illustrated in FIG. 6 is utilized to make the embodimentof the preform 26b shown in FIG. 3 or the embodiment 26c shown in FIG. 4by thermoforming a further sheet 48 of virgin polyethylene terephthalateto provide the further inner layer 32 that has a direct interface withthe inner layer 28 of polyethylene naphthalate such that the subsequentinjection molding is performed about the inner layers and can utilizepost consumer recycled polyethylene terephthalate while still having therequired thickness between the container contents and the recycledplastic. More specifically, the sheet 38 of polyethylene naphthalate andthe sheet 48 of virgin polyethylene terephthalate are thermoformed atthe thermoforming station 36 simultaneously with each other.Subsequently, the thermoformed sheets 38 and 48 of polyethylenenaphthalate and virgin polyethylene terephthalate are transferredtogether with each other to the mold 50 of the injection molding machine46 for the injection molding of the post consumer recycled polyethyleneterephthalate that provides the outer layer 30.

Apparatus 34b,c shown in FIG. 6 is utilized as illustrated with thesheet 38 of polyethylene naphthalate positioned above the sheet 48 ofvirgin polyethylene terephthalate as also shown in FIG. 7 so that thethermoforming is performed to provide the inner layer 32 of virginpolyethylene terephthalate between the inner layer 28 of polyethylenenaphthalate and the outer layer 30 of post consumer recycledpolyethylene terephthalate in accordance with the embodiment of thepreform 26b shown in FIG. 3.

Apparatus 34b,c shown in FIG. 6 is utilized with the respectivepositions of the sheet 38 of polyethylene naphthalate and the sheet 48of virgin polyethylene terephthalate reversed as illustrated in FIG. 8such that the thermoforming is performed to provide the inner layer 28of polyethylene naphthalate between the inner layer 32 of virginpolyethylene terephthalate and the outer layer 30 of post consumerrecycled polyethylene terephthalate.

With combined reference to FIGS. 5 and 6, the thermoforming station 36has lower and upper mold members 52 and 54 which are moved between theopen phantom line indicated positions and the closed solid lineindicated positions along the directions of arrows 56 and 58 to performthe thermoforming and then release the thermoformed inner layer orlayers for the trimming and subsequent injection molding. It should benoted that multiple preform inner layers are simultaneouslythermoformed, trimmed and then injection molded for efficiency. Morespecifically, the thermoforming is most efficiently performed inmultiple numbers that facilitate effective transfer to the particularinjection molding machine 46 where multiple preforms are injectionmolded. Each cycle of the thermoforming commences with the lower andupper mold members 52 and 54 in their phantom line indicated positionswhereupon movement of these mold members toward each other forms theheated sheet into the inner layer 28 of polyethylene naphthalate byitself as shown in FIG. 5 or along with the further inner layer 32 ofvirgin polyethylene terephthalate as shown in FIG. 6, preferably withmultiple formings taking place upon each stroke as described above.

With further reference to FIGS. 5 and 6, after the thermoforming aspreviously described, the sheet 38 of polyethylene naphthalate by itselfas illustrated in FIG. 5 or along with the sheet 48 of virginpolyethylene terephthalate as illustrated in FIG. 6 is moved by theassociated rolls 42 to the trimming station 44 where lower and uppertrimming members 60 and 62 are located. These lower and upper trimmingmembers 60 and 62 are moved toward and away from each other asillustrated by arrows 64 and 66 such that sharp cutters 68 thereofseparate the upper open end of each inner layer from the rest of theassociated sheet. The lower member 60 preferably has vacuum passages 70through which a vacuum is drawn to hold the trimmed inner layers to thismember prior to transfer thereof by a suitable actuator 72 to theinjection molding machine 44 where positioning of each inner layerwithin the mold 50 thereof for the injection molding of the outer layer30 of polyethylene terephthalate as previously described.

The polyethylene terephthalate multi-layer preforms 26b and 26crespectively, illustrated in FIGS. 3 and 4 have an outer layer 30 ofpost consumer recycled polyethylene terephthalate which by weight isgreater than about 75% of the total weight of the preform, as comparedwith a maximum of about 50% with conventional preforms. In the preferredconstruction of the preforms 26b and 26c, the injection molded outerlayer 30 of post consumer recycled polyethylene terephthalate by weightis greater than about 85% of the total weight of the preform, is mostpreferably in the range of about 88-92% of the total weigh of thepreform, and optimally is about 90% of the total weight of the preforms.More specifically, the construction of the multi-layer preforms 26b and26c with the inner layer 28 of polyethylene naphthalate and the innerlayer 32 of virgin polyethylene terephthalate both thermoformed allowsthe greater use of post consumer recycled polyethylene terephthalate forthe outer layer 30 than has been possible in the past.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative ways of practicing the invention asdescribed by the following claims.

What is claimed is:
 1. A method for making a multi-layer preform usedfor plastic blow molding, the method comprising:thermoforming a sheet ofpolyethylene naphthalate to provide an inner layer that functions as agas barrier; and injection molding an outer layer of polyethyleneterephthalate around the inner layer of polyethylene naphthalate whichlimits the transmission of gas through the outer layer of polyethyleneterephthalate upon blow molding of the preform into a container.
 2. Amethod for making a multi-layer preform used for plastic blow molding asin claim 1 wherein the injection molding of the outer layer is performedwith virgin polyethylene terephthalate that has a direct interface withthe inner layer of polyethylene naphthalate.
 3. A method for making amulti-layer preform used for plastic blow molding, the methodcomprising:thermoforming a sheet of polyethylene naphthalate to providean inner layer that functions as a gas barrier as well as permitting hotfilling; transferring the thermoformed inner layer of polyethylenenaphthalate to an injection mold; and injection molding within theinjection mold an outer layer of polyethylene terephthalate around theinner layer of polyethylene naphthalate which limits the transmission ofgas through the outer layer of polyethylene terephthalate upon blowmolding of the preform into a container.
 4. A method for making amulti-layer preform used for plastic blow molding, the methodcomprising:thermoforming a sheet of polyethylene naphthalate to providean inner layer that functions as a gas barrier; transferring thethermoformed inner layer of polyethylene naphthalate to an injectionmold; and injection molding within the injection mold an outer layer ofvirgin polyethylene terephthalate with a direct interface with the innerlayer of polyethylene naphthalate which limits the transmission of gasthrough the outer layer of polyethylene terephthalate upon blow moldingof the preform into a container.